1.About 真机
1.1 Xcode真机沙盒下载错误:Failed to download application container An error occured while attempting to download
解决：
真机沙盒查看内容下载时出现
Failed to download application container
An error occured while attempting to download the container from application "app" on "“XXX”的 iPhone" to "/Users/duanjichao/Documents/xxxx.xcappdata"
删除掉App 然后重启手机设备 重新运行App后即可
2.方法小记
2.1 ios中设置N秒后执行一个函数
设置N秒后执行一个函数，最常用的是设置一个定时器。
5秒后执行pushSecondController这个函数
[self performSelector:@selector(pushSecondController) withObject:nil afterDelay:5.0f];
比如：在第一个视图出现后5秒就跳转到第二个视图，代码如下：
- (void) pushSecondController{ SecondViewController *secondController = [[SecondViewController alloc] initWithNibName:nil bundle:NULL]; [self.navigationController pushViewController:secondController animated:YES]; }
- (void) viewDidAppear:(BOOL)paramAnimated{ [super viewDidAppear:paramAnimated]; [self performSelector:@selector(pushSecondController) withObject:nil afterDelay:5.0f]; }
5秒钟后又跳回第一个页面
- (void) goBack{ [self.navigationController popViewControllerAnimated:YES]; }
- (void) viewDidAppear:(BOOL)paramAnimated{ [super viewDidAppear:paramAnimated]; [self performSelector:@selector(goBack) withObject:nil afterDelay:5.0f]; }
2.2.1 连接字符串
NSArray *names = @["Hildr", @"Heidrun", @"Gerd", @"Guðrún", @"Freya", @"Nanna", @"Siv", @"Skaði", @"Gróa"];
NSString *result = [names componentsJoinedByString:@", "];
NSLog(@"%@",result);
打印结果：Hildr, Heidrun, Gerd, Guðrún, Freya, Nanna, Siv, Skaði, Gróa
2.2.2 “%”显示
如果想在NSString中显示双引号，一般是用转义字符，如 " ；
如果想在NSString中显示%就需要用%%,如：
NSString *strTest = [NSString stringWithFormat:@"%f%%",0.25];
NSlog("%@",strTest);
最后在控制台就会显示： 0.25％
Xcode 报错
“...xxx.app:resource fork, Finder information, or similar detritus not allowed”莫名其妙的错误！
1，关闭Xcode；
2，打开终端进入到‘DerivedData’目录：
cd ~/Library/Developer/Xcode/DerivedData/
3，在终端输入命令：
xattr -rc .
